This invention relates in general to tools for selectively removing material from metallic workpieces and in particular to a combined rough and finish metal cutting tool for forming an incomplete hole in a workpiece.
One of the oldest known and widely used manufacturing processes concerns the selective removal of material from a metallic workpiece. Many different tools are known for removing metal in various manners, such as by cutting, drilling, boring, and the like. A large number of such tools are specifically designed to remove metal in such a manner as to form a complete hole (i.e., a hole having a circular cross section, the diameter of which extends entirely within the workpiece) in the workpiece. The hole may extend completely through the workpiece, as with drilling, or it may extend only partially through the workpiece, as with counterboring. In either event, it is known to provide two or more of such metal removing tools on a single tool shank or support so that two metal removing operations may be performed with a single pass thereof. For example, the first metal removing operation may be the formation of a complete hole in the workpiece, while the second metal removing operation may be the formation of a counterbore co-axially aligned with the hole at the surface of the workpiece.
In some instances, rather than forming a complete hole in a workpiece, it is desirable to form an incomplete hole therein. An incomplete hole is a hole formed adjacent an edge of the workpiece such that a portion of such edge interrupts the otherwise circular cross section of the hole. In other words, a portion of the diameter of the hole being formed extends beyond the surface of the workpiece, resulting in an incomplete circular cross section. For example, in a vehicle differential case formed from two mating halves, incomplete holes having semi-circular cross sections may be formed in the opposite sides of each of the two halves. When the halves are secured together, the semi-circular incomplete holes are aligned to form opposed complete holes through the differential case so as to permit axle shafts to extend therethrough.
The formation of an incomplete hole in a workpiece poses certain difficulties which are not encountered in the formation of a complete hole. In particular, since the metal removing tool is not completely surrounded by the workpiece, as it is when a complete hole is being formed, the workpiece tends to deflect the tool sideways away from the workpiece and, therefore, away from desired axis of movement of the tool. This side loading of the tool is particularly troublesome when more than one tool is mounted on a single shank. In these instances, it has been found to be quite difficult to maintain precision in the removal of metal from the workpiece and still maintain a relatively fast and efficient operation.